1. FIELD OF THE INVENTION
This invention relates to a starter for discharge lamp, or more in particular to a starter for discharge lamp using a semiconductor switch element.
2. DESCRIPTION OF THE PRIOR ART
A widely used conventional starter for a discharge lamp having preheating electrodes or filaments employs a glow starter as shown in FIG. 1. In this drawing, reference numeral 1 shows an AC power supply, numeral 2 a ballast, numeral 3 a discharge lamp having filaments f.sub.1 and f.sub.2, numeral 4 a noise-blocking capacitor and reference character G a glow starter. When impressed with a voltage from the AC power supply 1, the glow starter G discharges thereby to temporarily close its contacts. During the temporary closure of the contacts, the filaments f.sub.1 and f.sub.2 are preheated. When the contacts of the glow starter G open again later, the ballast 2 produces a surge voltage whereby the discharge lamp 3 begins to glow. Upon completion of this discharge, the tube voltage drops, thereby preventing the glow starter G from discharging, so that the contacts of the glow starter G are kept open. Character S in the diagram shows a start switch.
The above-mentioned conventional glow-switch device has the disadvantages of a long starting time required and a short service life. Also, the glow starter often fails. Further, the glow switch is apt to promote the deterioration of the discharge lamp.